This invention relates to hot isostatic processing of compactible materials.
Uniaxial compaction in a heated die set (i.e. hot pressing), is a popular method of compacting metals, ceramics, and composites because of the economy with which shapes of accurate dimensions can be formed. The uniaxial compaction also offers benefits in the compaction of composite materials with planes oriented at right angles to the compaction axis. Pressing composites with this method avoids buckling of the fibers which could accompany an isostatic compaction technique. Because of the necessary pressures required for compaction of many materials, hot pressing is restricted to compaction of components of fairly small dimensions. As a practical matter, hot pressing is tonnage limited, i.e., the amount of compaction force per unit area (pressure) which can be delivered is tied to the size of the press.
Isostatic pressing generally is used to produce compacts in near net sizes and shapes of varied complexity, and is not tonnage-limited. Hot isostatic pressing (HIP) is performed in a gaseous atmosphere at substantially elevated temperatures, contained within a pressurization vessel. The pressure applied to the compacted material is the pressure in the HIP vessel, typically 15,000 psi. Initially, the charge to be pressed is placed or poured into and hermetically sealed within a receiver which is rigid at room temperature and then is enclosed within the pressurization vessel. The receiver, typically made of steel or other ductile metals, isolates the charge from the gaseous environment. The receiver deforms plastically under pressure at elevated temperatures, whereby the charge is simultaneously isostatically compacted and bonded. HIP produces complexly shaped compacts at near net shape with uniform density, and permits the fabrication of components 50-100 times greater in area than possible with mechanical pressing.